where \(s_{X,0}\)  is the estimated number of bits coming from vacuum events, \(s_{X,1}\)  is the number of bits originating from single photons, \(\epsilon _{s}\)  is the security parameter and \(h(x)=-x\log _2 (x)-(1-x)\log _2 (1-x)\)  is the binary entropy. A protocol is said to be \(\varepsilon =\epsilon _s +\epsilon _c\)  secure if it is \(\epsilon _c\) -correct and \(\epsilon _s\) -secret [1]}. For all calculations presented we use \(\epsilon _c =10^{-15}\)  and \(\epsilon _s =10^{-9}\) .
